Filters used for internal combustion engines, compressors, hydraulic systems and the like all have to be replaced from time to time as they become clogged with dirt and other contaminants. These contaminants can include heavy metal oxides. Such used filters are heavy with hydrocarbon liquids and present a problem with regard to disposal. Most filters contain metal casings and filter media which includes different filters generally within paper or plastic casings or inserts.
As well as petroleum filters, other types of filters that are contaminated with hydrocarbons also have to be disposed of when they have been used. Such filters may be made of charcoal, paper, or cloth. They may include filter media such as peat, sand or diatomaceous earth. Some filters may have plastic casings or the heavy casings are metal.
In the past these filters were buried in landfills. However, it has been determined that the leakage of oil out of used filters was not satisfactory and does not comply with the environmental disposal laws. Thus, initially it was decided that most of these filters should be crushed as much of the oil leaves the filters thus the hydrocarbon content of the filters could be reduced to the order of 8% to 12%. Furthermore, the crushing step reduces the volume of such filters thus requiring a smaller disposal volume, also some of the oil could be recovered and passed for recycling.
Whereas the crushing step was clearly an improvement inasmuch as the oil content was reduced, the crushed filters could still not be recycled as their hydrocarbon content was still too high. Furthermore, because of the hydrocarbon content, shipping of such filters comes under a special waste category requiring a special licence, and furthermore landfills are not accepting used filters having a hydrocarbon content greater than 3%.
To overcome this problem the crushed used filters were heated in a furnace to burn off the hydrocarbons. However, this step generally resulted in excessive black smoke due to incineration of the hydrocarbons which are not acceptable to the Canadian and U.S. Clean Air Act requirements on stack emissions. When such filters were incinerated, hydrocarbons turned to ash and carbon dioxide, carbon monoxide gases, together with heavy metal oxides and other solids and gases exited from the stack. Whereas scrubbers may be used with such a system to remove solid particles such as ash, the disposal of such ash still presented certain environmental problems. The result of incinerating the crushed used filters reduced the hydrocarbon content below 3%, thus it was now found that the incinerated crushed filters which contained primarily a mixture of steel and other metals may be recycled in steel mills and the like.